Hank: If you know any kids -- or remember being one yourself -- you might know that they can be an active bunch. They tend to do a lot of running around, bouncing off of walls, and just generally trying to get places without always looking where they’re going. Which can mean a lot of scraped knees and elbows. And sometimes, hydrogen peroxide.

A lot of people use hydrogen peroxide to clean wounds, and it isn’t exactly pleasant: in addition to making the scrape hurt even more by activating the receptors that make you feel pain, the wound gets all weird and bubbly. But the reason it bubbles is also the reason you probably shouldn’t be using it to clean wounds -- even though hydrogen peroxide is really, really good at killing bacteria. If anything, it’s too good.

Peroxide kills bacteria by attracting the electrons from their cellular membranes, breaking the membranes open. That fizzing you see? That’s mostly the peroxide reacting with an enzyme inside the bacteria, called catalase, forming water and oxygen gas. Problem is, hydrogen peroxide is such a great antiseptic because it doesn’t care what kinds of cells it destroys. So, peroxide will kill your cells, too! It rips through their membranes like they were just run-of-the-mill, scrape-knee bacteria. And it’ll also make your cells fizz, because your cells also have catalase in them.

Why? Because your body actually makes hydrogen peroxide on its own! Your cells produce it as waste when they process sugar. So your cells are stocked with catalase to help turn that hydrogen peroxide into water and oxygen before it can do any harm. But, when peroxide comes at your cells from the outside, the catalase can’t protect them. So, when you pour peroxide on a cut, and it starts to fizz, it’s not only killing bacteria -- it’s also killing some of your healthy cells. Like the cells that were gonna help heal the wound.

So what should you do if you or your kid skins a knee? Well, first of all, if it’s anything major or you’re concerned for any reason, I’m obligated to tell you to call your doctor. But for scrapes you’re treating at home, most doctors and researchers wouldn’t recommend using an antiseptic at all -- cold water, and maybe some soap, is enough to clean it.

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